1. Field of the Invention
The present invention relates generally to a pressure sensor and, more particularly, to a pressure sensor that is provided with a thermally conductive member disposed between a heat producing portion of a pressure sensor die and one or more electrical leads which are used to dissipate the heat in cooperation with heat dissipation through the housing structure of the pressure sensor structure.
2. Description of the Prior Art
Many different types of pressure sensors are well known to those skilled in the art. One particular type of pressure sensor comprises a silicon die that has a first surface and a second surface. The first surface comprises a relatively thin layer of material, such as or silicon nitride. The second surface is partially etched to form a cavity through a portion of the thickness of the die. Since the cavity in the second surface does not completely penetrate through the thickness of the die, a portion of the first surface extends, as a diaphragm, over the cavity. Piezoresistive components are disposed on the diaphragm and are sensitive to distortions of the diaphragm in response to pressure changes.
Certain pressure sensor applications also incorporate a plurality of electronic components formed in a portion of the first surface of the sensor die. These electronic components form amplification and linearization circuits that are connected in signal communication with the piezoresistive components on the diaphragm. In applications of this type, the electronic components produce heat which must be dissipated so that the pressure sensor die is not adversely affected by the temperature changes that could otherwise occur as a result of the heat produced by the integrated circuit comprising the electronic components.
U.S. patent application Ser. No. 07/962,641, which was filed by Maurer on Oct. 16, 1992 and assigned to the assignee of the present application, discloses a pressure sensor that is specifically adapted for use with a component carrier. It is provided with a housing member that is attached to a rigid and generally planar member, such as a ceramic circuit board. The legs of the housing member can pass through holes in the circuit board or, alternatively, can attached to edges of the board. The legs of the housing are provided with bails which have steps shaped to seize the circuit board after the legs are flexed to permit insertion of the board between them. The housing is provided with an opening that is shaped to receive a media seal, a pressure sensor die and a conductive seal between a surface of the opening and a surface of the ceramic circuit board. When the circuit board is attached to the housing, the seals and the pressure sensor die are compressed therebetween to provide good fluid sealing association between the components and to also provide electrical communication between the components on the pressure sensor die and the components on the circuit board. An alternative embodiment of the sensor comprises two housing members that are attached to opposite sides of the same circuit board so that a differential pressure sensor can be provided.
U.S. Pat. No. 4,656,454, which issued to Rosenberger on Apr. 7, 1987, discloses a piezoresistive pressure transducer with elastomeric seals. A piezoresistive stress sensitive element in the form of a diaphragm of semiconductor material is provided with a thickened rim to hold the diaphragm between a pair of premolded elastomeric seals in a thermoplastic housing. Electrical connections with external circuitry are made with strain relief jumpers which connect conductive regions on the element outside the seals to conductors which pass through the housing wall.
Selectively conductive elastomeric components are available in commercial quantities from Fujipoly and are referred to as the low resistance ZEBRA elastomeric connectors. They are constructed of alternating parallel layers of electrically conductive and nonconductive silicon elastomer. The electrically conductive layers are filled with silver-metal particles. The low resistance elastomeric connectors of this type provide a redundant connection with a minimum of two conductive layers recommended for each printed circuit contact pad. The connectors are available with an insulating barrier or silicon supports. The connectors are used for connecting electroluminescent and plasma type displays to printed circuit boards or for connecting hybrid circuits to printed circuit boards. In the Dec. 7, 1989 edition of EDN Magazine, an article titled "Elastomeric Connectors" by J. D. Mosley describes elastomeric connectors and many different types of applications where they can be used. Several sources of these connectors, such as Fujipoly and Elastomeric Technologies, are discussed in this article along with many different types of connectors provided by the suppliers.
In the Dec. 4, 1972 edition of "Electronics" magazine, an article titled "Integration Brings A Generation Of Low-Cost Transducers" was written by Arthur R. Zias and William F. J. Hare. This article discusses pressure transducers which use an all silicon vacuum reference chamber and a Wheatstone bridge arrangement of diffused piezoresistive resistors to measure pressures over a large range.
The thermally conductive and electrically insulative component which is utilized by the present invention is a commercially available component. It can be purchased from the Bergquist Company under the name "SIL-PAD".
The elastomeric components described above are well known to those skilled in the art. Although many different techniques are used to provide the selective conductivity of the elastomeric connectors, they share a common characteristic of conducting electrical current in one direction through their thickness while preventing the conduction of electric current in other directions through the elastomeric member. The thermally conductive elastomeric material described above is electrically insulative in all directions through its structure. These materials are all available in commercial quantities from several different suppliers. Although the elastomeric portions of the present invention, as will be described below, are arranged in a particular configuration to specifically suit the needs of the present invention, it should be clearly understood that each of the separate portions of the elastomeric elements of the present invention are individually known to those skilled in the art and to those companies that manufacture the various forms of elastomeric materials.
U.S. patent application 07/961,994, which was filed by Maurer on Oct. 16, 1992, and assigned to the assignee of the present application, describes a force sensor that incorporates a pressure transducer disposed within a housing structure. A force transmitting means, such as a shaft which is slidably disposed within an opening, is provided to communicate force from an external source to a diaphragm of a pressure sensor. An elastomeric conductor is disposed between electronic components on the diaphragm of a pressure sensor die and conductive leads that are used to communicate signals from pressure sensor die to components which are disposed externally relative to the force sensor.
U.S. Pat. No. 5,184,107, which issued to Maurer on Feb. 2, 1993 discloses a low cost piezoresistive pressure transducer which utilizes premolded elastomeric seals in which at least one seal is electrically conductive. A piezoresistive stress sensitive element in the form of a diaphragm of a semiconductor material is provided with a thickened rim and is held at its rim between a pair of premolded elastomeric seals in a two piece housing. Electrical connections with external circuitry are made by conductive paths through one of the elastomeric seals which makes contact with electrical leads which pass through a housing wall.